To a large extent the child might just be imitating your lifestyle. Most parents themselves are couch potatoes, who just want to either hit the sack, watch TV etc. So, first try encouraging by going out to play with him, else sent him
to a sports academy, encourage him to take part in sports activities at school.
Finally, make a comment like, son it would be nice if you played soccer in the field, rather than watch soccer on TV.

Hi,
Please show your son sports channel of his interest,as much as possible.Then make him play it.Try to project all the advantages of the sports like,money ,fame ,fitness,etc.
Show him the disadvantages of playing only with the toys.Initially its hard to change from easygoing toys to hardworking sports.Give him a spotrs friend.

Hey man!
how are you?
sometimes hard steps are needed to be taken! Sports are better for your child then TV so you need to tell him that son you can watch 2 hours of TV and then you have to go out and play with the children of your own age...
hey man its for his own good....!!!
bye

If your son shows any intrest in sports then you must encourage that even if it is something like figure skating (which is a sport mind you) I thinkn sports or some other sort of recreational activiy that stimulates the body is key to developing a well rounded person, however if someone is not interested in playing sports then it cannot be forced upon them, and it would be wrong to try and do so, but it is still a good idea for them to get out of the house and do something active other than just sitting around the house playing video games and what not.